1. Field of the Industrial Application
This invention relates to a film magnetic head which provides a high reproduction output suitable for use in high density magnetic recording.
2. Description of the Prior Art
A film magnetic head has been developed to increase the magnetic recording density and the frequency at which a magnetic recording medium such as a magnetic disc and a magnetic tape may be used. An induction type film magnetic head base on electromagnetic induction comprises upper and lower magnetic pole films which form a magnetic circuit with a magnetic gap. A coil conductor film which crosses the magnetic circuit, and insulating films for magnetically and electrically insulating coils from one another and a magnetic pole and a coil from each other are provided. These films are formed and laminated using a film forming technique and a precision machining method.
In addition, a magnetoresistance effect type (or MR type) film magnetic head has been proposed in which a magnetoresistance effect element is provided in a magnetic circuit formed by a magnetic core similar to that described above.
In general, these film magnetic heads employ a small magnetic core made up of a soft metal magnetic film. Accordingly, in these film magnetic heads, the magnetic core loss at high frequency, such as eddy current loss is low, and the magnetic circuit is compact in comparison to bulk type magnetic heads. This results in an improvement in the recording and reproducing efficiency in a magnetic recording and reproducing operation over a wide range of frequencies. On the other hand, the induction type film magnetic head is made up of a small magnetic core and a small winding, and therefore it is a low impedance magnetic head suitable for a high frequency, high density magnetic recording operation.
The electromagnetic conversion characteristic of such a film magnetic head depends heavily on the magnetic characteristic of the magnetic pole film employed. That is, a magnetic pole film high in saturated flux density is necessary for recording signals on a high coercive force medium in order to permit the recording of short wavelengths, and in order to efficiently record and reproduce high frequency signals with high fidelity, a high magnetic permeability should exist with a high frequency range.
In order to improve the magnetic permeability with the high frequency range, in the magnetization process a magnetization revolution with high switching speed should be employed rather than a magnetic domain wall movement. Accordingly, it is necessary that a uniaxial magnetic anisotropy be established in the magnetic film so that the easy axis is aligned in the track widthwise direction of the film magnetic head, whereby the hard axis direction coincides with the excitation direction.
If the uniaxial magnetic anisotropy is excessively large, then the gradient of the magnetization curve along the hard axis direction decreases. If on the other hand, the uniaxial magnetic anisotropy is excessively small, then magnetic domain wall movement is liable to occur, resulting in a decrease in the magnetic permeability in the high frequency range. That is, although the most suitable uniaxial magnetic anisotropy exists, the most suitable conditions for achieving it cannot be determined simply, since it depends not only on the uniaxial magnetic anisotropy but also on the configuration of the magnetic core in the magnetic head.